1. Field of the Invention
The present invention relates generally to a component mounter, and more particularly to a head assembly for a component mounter.
2. Description of the Related Art
As is known in the surface mount technology (SMT) art, a component mounter receives various components from a component supplier, feeds the received components to certain positions of a printed circuit board (PCB), and mounts the components on the PCB.
In general a component mounter includes: a component supplying part that supplies electronic components to be mounted, a conveyor part that carries a PCB on which the electronic components are to be mounted, and a head assembly that successively picks up the electronic components from the component supplying part and mounts the electronic components on the PCB.
Recently, a plurality of nozzle spindles installed on a head assembly of the component mounter is provided to either successively or simultaneously pick up a plurality of electronic components, move the plurality of electronic components to a conveyor part simultaneously, and either successively or simultaneously mount the plurality of components on a PCB in an effort to improve the efficiency of a component mounter.
However, by increasing the component mounter's efficiency through increasing the number of nozzle spindles, the total size of the head assembly increases as well. Therefore, there is a trade-off in increasing the number of nozzle spindles installed on the head assembly.
Various known component mounters attempt to increase mounting efficiency without unduly increasing the size of the head assembly. For example, as illustrated in FIG. 1, a head part 10 disposed on a component mounter disclosed in Japanese Patent Laid-Open Publication No. hei 2003-273582 includes three revolving head assemblies 11 that are aligned. A number of nozzle spindles 40 are disposed in a generally circular arrangement in each head assembly 11 so that the spindles 40 of each head assembly 11 are rotated about a common vertical central axis by a corresponding nozzle rotating mechanism 60. Pickup nozzles 50 are coupled to lower portions of the nozzle spindles 40. The nozzle spindles 40 of the respective head assemblies 11 are selected by nozzle selecting mechanisms 70, and lowered by nozzle lifting mechanisms 80. The head assemblies 11 are fixed to a head frame 12.
The head assemblies 11 of the component mounter 10 will be described in further detail with reference to FIG. 2. One head assembly 11 includes a plurality of nozzle spindles 40 installed in a circular orientation about a spline shaft 35.
A nozzle holder 50 is coupled to the spline shaft 35. The nozzle spindles 40 are disposed to move up and down in the same circle about the spline shaft 35 of the nozzle holder 50.
The spline shaft 35 rotates according to the operation of a nozzle rotating mechanism 60, which generally acts as a nozzle rotating motor, and accordingly, the nozzle spindles 40 and the nozzle holder 50 coupled to the spline shaft 35 rotate.
In the meantime, to individually select and lower one of the nozzle spindles 40, the nozzle selecting mechanism 70 and the nozzle lifting mechanism 80 are disposed on the head assembly 11. The nozzle selecting mechanism 70 includes a compressed air supply chamber 71 and a nozzle selecting valve 72 for controlling the injection of compressed air into a pressurized air supply chamber 32 corresponding to a selected nozzle spindle 40. Here, the pressurized air supply chamber 32 is a space formed inside an air cylinder block 30 that is coupled to the head assembly 11 and disposed on the nozzle holder 50, and can be connected to each of the nozzle spindles 40.
Accordingly, if air under positive pressure is introduced into the pressurized air supply chamber 32 disposed on the selected nozzle spindle 40, a piston 52 formed in the pressurized air supply chamber 32 and an air cylinder shaft 53 coupled under the piston 52 are lowered, such that a lower end 53a of the air cylinder shaft 53, an upper end 50a of the selected nozzle spindle 40 attached to the lower end 53a, and a top surface 85a of a stepped portion of a spline nut 85 are positioned at the same level, resulting in making the air cylinder shaft 53, the nozzle spindle 40, and the spline nut 85 integrated into one body. Here, the spline nut 85 is coupled to the nozzle lifting mechanism 80 including a cam follower 84, an eccentric cam 82, and a driving motor 81, such that the spline nut 85 can vertically move. Thus, the nozzle spindle 40 coupled to the spline nut 85 can be lowered.
Further, a vacuum suction unit 90 helps the nozzle spindles 40 to pick up electronic components. The vacuum suction unit 90 causes air under negative pressure from a negative pressure air supply chamber 91 to be individually provided into the nozzle spindles 40 by picking up-and-mounting valves 92 installed outside the nozzle holder 50, such that the nozzle spindles 40 can individually pick up the electronic components.
As can be appreciated from the foregoing, revolving head assemblies have a small size and can mount a plurality of electronic components. However, the conventional head assembly 11 for the component mounter employs the nozzle lifting mechanism 80 including the eccentric cam 82, the cam follower 84, and the spline nut 85 to lower the nozzle spindles 40, thereby resulting in a complex lifting mechanism and a low mounting speed.
Furthermore, since the number of air cylinder shafts 53 directly corresponds with the number of nozzle spindles 40, the size of the head assembly 11 is increased so that it may be difficult to pick up and mount a plurality of components simultaneously, thereby decreasing a mounting speed of the assembly 11.
Moreover, since the head assembly 11, which includes the eccentric cam 82, the cam follower 84, and the spline nut 85, employs a number of picking up-and-mounting valves 92 in direct correspondence with the number of nozzle spindles 40, the total weight of the head assembly 11 is increased, and the head assembly 11 occupies a considerable space so that the assembly 11 may be difficult to be applied to various work conditions.